This invention relates to tire changing apparatus.
In U.S. Pat. No. 3,255,800 issued June 14, 1966 to Strang, et al, there is disclosed a tire changing apparatus which has been manufactured and sold in considerable quantity over the years and has achieved considerable commercial success. The apparatus loosens both upper and lower beads of a tire on a wheel received on a tire changing table as well as drives a tire changing tool.
In the process of a bead loosening operation, an upper bead loosening assembly is manually positioned with respect to the upper bead of a tire prior to actuation of the machine. The upper bead loosener assembly includes a shoe which is engaged with the upper bead, a mounting shaft for the shoe which is selectively engageable with a lever driven by a motor, and a nose formation which is disposed on the inner surface of a wheel to properly orient the shoe prior to engergization of the motor.
While the bead breaker assembly is composed of a number of parts, they are all interconnected and as a consequence, the entire assembly must be supported during the positioning process. Because of the number of parts involved, the weight of the assembly is not inconsequential and in a high volume operation, the user of the apparatus may experience some fatigue during the course of positioning the upper bead loosener assembly.
As a consequence, in order to minimize the weight of the upper bead loosener that must be shifted to achieve positioning, it has been proposed to affix the shoe mounting shaft to the power system of the apparatus so as to be supported thereby while providing an adjustable connection between the shoe and the shaft. In the usual case, the shaft extends generally vertically so a first adjustable connection is provided so that the initial height of the bead loosening shoe may be adjusted in the vertical direction for wheels of differing widths. Because wheels also have varying diameters, it is necessary to provide a second adjustable connection whereby the shoe may be adjustably positioned generally radially of the wheel.
While such a proposal minimizes the weight that must he shifted by the operator, it poses numerous disadvantages. For one, in the usual case, at least one of the adjustable connections must be locked prior to actuation of the apparatus requiring an effort to be expended by the operator in locking the connection. This is, of course, time consuming to some degree and lengthens the time required to perform each tire changing operation.
Moreover, in apparatus wherein the drive for the upper bead loosener is linked mechanically to the tool driving shaft, it will be appreciated that when a tool is driven by the apparatus, the upper bead loosener will be in motion, even though unneeded, and may pose a hazard to the operator or bystanders in the immediate vicinity of the apparatus. Thus, while a weight reduction is achieved, it is made only at the expense of time and safety.
In many instances, such tire changing apparatus have been provided with means for limiting the movement of the lower bead loosening shoe, particularly when the apparatus is designed for accomodating wheels of vastly varying diameters, particularly, small diameter wheels. Those skilled in the art will readily recognize that the lower bead loosener must have a relatively long throw for small wheels such as ten inch wheels in order to change them successfully. However, if the long throw is maintained for wheels of all sizes, there is the very real possibility that for larger wheels, the lower bead loosener will come into contact with the drop center of the wheel and the continued application of force will cause damage to the lower bead loosening shoe, the wheel, or both. Wheel and/or shoe damage may also occur when wheels having narrow rims are serviced for essentially the same reason.
As a consequence, many tire changing machines have been provided with a stroke limiter which may be in, for example, the form disclosed in U.S. Pat. No. 3,398,777 issued Aug. 27, 1968 to Strang. Such stroke limiting means have proved to be very effectual but require a fair number of components thereby contributing to the expense of the apparatus.